Oil such as lubricant oil, hydraulic fluid, turbine oil and the like is used for various machinery or equipment. Degradation of oil causes breakdowns of or troubles with machinery and the like. Concretely, oil comes to the end of its life when oil-degradation-states reach a certain level, and using machinery and the like with such dead oil as it is will raise possibility of causing troubles with the machinery and the like. Therefore, monitoring oil degradation states is a key for preventing the troubles from occurring. Specifications related to such monitoring have been established and various technologies related to such monitoring have been proposed.
ASTM D1500 is known as one of conventional test methods for estimating life expectancy of oil by colors of oil itself. The method uses one of oil characteristics that colors of oil turn from yellow, to red, to reddish brown, and to blackish brown, and estimates oil is reaching its end of the usefulness (oil is being degraded) when a color of oil becomes almost black. However, smooth or hydraulic operations with machinery are not brought by the color characteristic of oil but brought by oil-lubricant characteristics such as oil viscosity and the like. Lubrication-property or operability-property of oil does not directly relate to colors of oil; therefore, estimating life expectancy of oil requires examination of oil for its contamination level.
Methods for examining oil contamination levels include the one according to the number of particles per each particle size-group and the one measuring weight of contaminants in oil. Representative methods of the former are NAS1638, ISO 4406, and JIS B9930, and those of the latter are ASTM D4898 and JIS 139931.
In addition, methods for estimating life expectancy of oil include ASTM D943 (commonly called as TOST) and ASTM D2272 (RPVOT test method). These days, a trend of decreasing sizes of oil tanks for machinery has been growing from a resource saving-perspective; therefore, even if oil which passed in the foregoing methods is employed for machinery, the number of cases that the oil does not work due to increase of oxidation products in the oil has been increasing. In order to solve this problem, a voltammetric method (ASTM D6810) which measures amount of antioxidant remained in oil came into use.
Besides, the following technique has been proposed. (Refer to Patent literature 1 as the example): A photometer section of a color-difference meter is directly inserted into lubricant oil in an oil tank for measuring the lubricant oil-color changes. Then, an alarm device activates when a value of the measured-oil color change exceeds the predetermined value.
Moreover, the following device, a device for simple estimation of lubricant oil-life expectancy, has been proposed. (Refer to Patent literature 2 as the example): The device for simple estimation of lubricant oil-life expectancy includes a container whose shape is designed to hold lubricant oil in a predetermined thickness. The device includes a color chart which is laid on the inside face of the container that can be seen with human eyes from the outside of the container in the through-thickness direction, and which is colored with a plurality of color-samples gradated along with lubricant oil-degradation. The device for simple estimation of lubricant oil-life expectancy judges lubricant oil-degradation levels by estimating lubricant oil-life expectancy according to relation between visible colors and invisible colors in the color chart with human eyes with the estimated-lubricant oil being held in the container.
Furthermore, the following device, a lubricant oil-degradation-monitoring device, has been proposed. (Refer to Patent literature 3 as the example): The lubricant oil-degradation-monitoring device includes a mean for sensing visible radiation which penetrates lubricant oil dividing the visible radiation into three primary colors and a mean for detecting absorbance of each of the three primary colors in the lubricant oil according to detection signals outputted from the foregoing mean for sensing the visible radiation. The lubricant oil-degradation-monitoring device reads lubricant oil-degradation levels according to the detected absorbance.
Besides, the following method, a lubricant oil-degradation level-estimation method, has been proposed. (Refer to Patent literature 4 as the example): The lubricant oil-degradation level-estimation method emits light into a lubricant oil-specimen which is put in a specimen cell. The light which penetrates the lubricant oil-specimen is divided into three light. Then, after penetrating a filter, each of the divided light is converted into electrical signals and expressed as tristimulus values of colors. Points of evaluation on the lubricant oil are given according to a chromatic coordinate gained from one of the tristimulus values and the tristimulus values and according to a constant number preset for each lubricant oil-specimen-type. A degradation and contamination state of the lubricant oil-specimen is judged according to the points of evaluation on the lubricant-oil.
In addition, a method for measuring degradation levels of lubricant oil and lubricant agents as well as a simple measurement instrument and an automatic measurement instrument related to the foregoing method have been proposed. (Refer to Patent literature 5 as the example): In Patent literature 5 as one of the examples of the method for measuring oil degradation levels, a specimen of lubricant oil or lubricant agents is applied to a flat surface-part of an instrument, which maintains almost constant roughness, for judging the oil degradation levels. Then, the applied specimen is nearly evenly leveled. The degradation level of the lubricant oil or the lubricant agents is judged according to a blackening level of the flat surface-part colored with the evenly leveled-specimen.
Several other techniques related to estimating life expectancy of oil have been introduced. (Refer to Patent literature 6 as the example.) The inventors who made the present application had also reported several research results on estimation of life expectancy of oil (Refer to Non patent literature 1).